1. Field of the Invention
The present invention relates to an image-processing unit that generates a high dynamic range image using a single set of image data.
2. Description of the Related Art
Various imaging apparatuses, such as digital still cameras, video cameras, electronic endoscopes, etc., which capture scenes or subjects are commonly known. Imaging apparatuses generate an image signal corresponding to a captured scene or subject. The generated image signal is digitized into image data. The image data undergoes predetermined data processing, and then is transmitted to a monitor to be displayed as an image, or transferred to a memory for storage.
Image data to be transmitted to an all-purpose monitor is generally standardized to 8-bit digital data. Accordingly, an image corresponding to the standardized image data comprises a plurality of pixels whose luminance value varies from 0 to 255.
The larger the luminance difference between neighboring pixels, the clearer the shade and contour of a subject will be in a displayed image. Accordingly, if the difference between minimum and maximum luminance in a subject or a scene to be captured is small, a clear image with fewer overexposed or underexposed sub-images can be displayed by capturing the subject or the scene by adjusting the exposure such that the minimum and maximum luminance are 0 and 255, respectively. However, if the difference between minimum and maximum luminances is large, it is difficult to simultaneously display low and high luminance sub-images clearly.
To solve this difficulty, a high dynamic range image, hereinafter referred to as an HDR image, is known. Japanese Unexamined Patent Publication No. 2008-104009 discloses that the an HDR image may be rendered using image data generated based on a plurality of images of the same subject captured at diverse exposures.
However, in the HDR rendering disclosed by the patent Publication, since there are time lags while the subject is captured several times, the location of a moving subject shifts between successively captured images. As a result, an HDR image will be blurred.
In addition, in prior art HDR rendering, adequate sub-images are selected for every partial area of an entire image to be rendered among sub-images for the same partial area in images captured with varying an exposure. The adequate sub-image is selected by comparing the luminance of sub-images for a given partial area with a fixed threshold. However, the problem arises that a border, between sub-images neighboring each other selected from different captured images on the basis of comparison of luminance with the fixed threshold might, be displayed distinguishably.